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| United States Patent |
5,107,395
|
|
Kawakami
, et al.
|
April 21, 1992
|
Method of producing insulating oil comprising dibenzylbenzene
Abstract
An insulating oil comprising dibenzylbenzenes which is most suitably used
for impregnating a metallized plastic film capacitor, is produced by the
reaction of benzene or toluene with diphenylmethane or a methyl derivative
thereof at 170.degree. C. to 400.degree. C. in the presence of a synthetic
crystalline zeolite catalyst having a molar ratio of SiO.sub.2 to Al.sub.2
O.sub.3 of 20 or above, wherein the inlets of main pores are constituted
of ten-membered oxygen rings.
| Inventors:
|
Kawakami; Shigenobu (Ichikawa, JP);
Endo; Keiji (Yokohama, JP);
Dohi; Hideyuki (Yokohama, JP);
Sato; Atsushi (Tokyo, JP)
|
| Assignee:
|
Nippon Petrochemicals Company, Limited (Tokyo, JP)
|
| Appl. No.:
|
601797 |
| Filed:
|
January 7, 1991 |
| PCT Filed:
|
March 7, 1990
|
| PCT NO:
|
PCT/JP90/00295
|
| 371 Date:
|
January 7, 1991
|
| 102(e) Date:
|
January 7, 1991
|
| PCT PUB.NO.:
|
WO90/10686 |
| PCT PUB. Date:
|
September 20, 1990 |
Foreign Application Priority Data
| Current U.S. Class: |
361/315; 174/25C |
| Intern'l Class: |
H01G 004/22; H01B 003/24 |
| Field of Search: |
361/327,314,315,323
585/6.3,24,25
252/567
174/25 C
|
References Cited
U.S. Patent Documents
| 3481997 | Dec., 1969 | Vanderwerff | 260/670.
|
| 4568793 | Feb., 1986 | Sato et al. | 174/25.
|
| Foreign Patent Documents |
| 48-95599 | Dec., 1973 | JP.
| |
| 49-14320 | Feb., 1974 | JP.
| |
| 49-41634 | Apr., 1974 | JP.
| |
| 49-135199 | Dec., 1974 | JP.
| |
| 61-51704 | Mar., 1986 | JP.
| |
| 1579679 | Nov., 1980 | GB.
| |
Primary Examiner: Griffin; Donald A.
Attorney, Agent or Firm: Scully, Scott, Murphy & Presser
Claims
We claim:
1. A method of producing an electrical insulating oil comprising
dibenzylbenzenes which is produced by the reaction of benzene or toluene
with diphenylmethane or a methyl derivative thereof at a reaction
temperature of 170.degree. to 400.degree. C. in the presence of a
synthetic crystalline zeolite catalyst having a molar ratio of SiO.sub.2
/Al.sub.2 O.sub.3 of 20 or above, wherein the inlets of main pores are
constituted of ten-membered oxygen rings.
2. The method as claimed in claim 1, wherein said synthetic crystalline
zeolite is a ZSM-5 type catalyst.
3. The method as claimed in claim 1, wherein said ZSM-5 type catalyst is
ZSM-5.
4. The method as claimed in claim 1, wherein the molar ratio of said
benzene or toluene to diphenylmethane or its methyl derivative is 0.2 to
20.
5. The method as claimed in claim 1, wherein said reaction temperature is
200.degree. to 350.degree. C.
6. The method as claimed in claim 1, wherein said electrical insulating oil
is the one used for impregnating oil-filled electrical appliances.
7. The method as claimed in claim 6, wherein said oil-filled electrical
appliances are oil-filled capacitors.
8. The method as claimed in claim 7, wherein said oil-filled capacitors are
oil-filled metallized plastics film capacitors.
9. An oil-filled electrical appliance which is filled with insulating oil
prepared by the method as recited in claim 1.
10. The electrical appliance as claimed in claim 9, wherein said oil-filled
electrical appliance is an oil-filled capacitor.
11. The electrical appliance as claimed in claim 10, wherein said
oil-filled capacitor is an oil filled metallized plastic film capacitor.
Description
DESCRIPTION
1. Technical Field
This invention relates to a method of producing an electrical insulating
oil comprising dibenzylbenzenes. The insulating oil prepared according to
the present invention is suitably used for oil-filled electrical
appliances in which at least a part of insulating material of dielectric
material is made of a plastic film. It is used more preferably for
oil-filled capacitors, especially suitable for oil-filled metallized
plastic film capacitors.
2. Background Art
The reduction of sizes and weights of oil-filled capacitors and oil-filled
cables are recently eagerly required. In order to comply with the
requirement, the insulating materials or dielectric materials are, at
least partially, made of plastics, for example, polyolefin such as
polypropylene.
In spite of the attempt to improve the structure itself of oil-filled
electrical appliances, there is no satisfactory improvement in the
electrical insulating oil to be used for impregnation. In other words, for
example, the conventional insulating oils such as refined mineral oils,
polybutenes, alkylbenzenes, diarylalkanes, alkylbiphenyls and
alkylnaphthalenes are not always satisfactory in view of their properties
and characteristics. Under the existing circumstances, there are few
electrical insulating oils which are suitable for the oil-filled
electrical appliances such as oil-filled capacitors, especially
metallized-film capacitors (hereinafter referred to as "MF capacitor") in
which a metallized film made by depositing a metal such as aluminum is
wound as an electrode and an electrical insulating oil is impregnated.
That is, presently used MF capacitors are mainly the so-called dry-type MF
capacitors which are not impregnated with an electrically insulating
material such as insulating oil. In capacitors as well as in other
electrical appliances, the potential gradient is generally high when an
electrically insulating material exists around electrodes or conductors.
Accordingly, the voltage-withstanding property of an impregnated MF
capacitor is higher than that of a dry-type capacitor and the former
capacitor can comply with the requirements for reducing the sizes and
weights of capacitors. Nevertheless, the metallized film using a plastic
base film such as polypropylene film receives a large influence of oil
impregnation. For example, the size of base film is changed by oil
impregnation and even when impregnation oil slightly permeates between a
deposited metal layer and a base film, deposited metal layer is creacked,
and what is worse, the deposited metal film is often peeled off, which
results into dielectric breakdown. Accordingly, the electrical insulating
oil suitable for MF capacitors is few.
For example, in an MF capacitor which is impregnated with benzyltoluene or
phenylxylylethane, the capacity is lowered severely in use and the corona
(partial) discharge characteristic is not always good.
DISCLOSURE OF THE INVENTION
The present invention relates to a method for producing electrical
insulating oil which is characterized in that benzene or toluene is
reacted with diphenylmethane or its derivative at a reaction temperature
of 170.degree. to 400.degree. in the presence of a synthetic crystalline
zeolite catalyst having a molar ratio of SiO.sub.2 to Al.sub.2 O.sub.3 of
20 or above, wherein the inlets of main pores are constituted of
ten-membered oxygen rings.
The present invention will be described in more detail in the following.
A method to produce xylene by the disproportionation between toluene
molecules in the presence of ZSM-5 type zeolite catalyst (British Patent
No. 1,463,359). This is naturally accomplished by transfer of methyl
groups.
When dibenzylbenzene is produced from toluene and diphenylmethane using
ZSM-5 type zeolite, assuming that the transfer of methyl group is caused
to occur, the formation of xylene is naturally presumed because toluene
exists. If xylene is produced, it is not desirable because the yield of
dibenzylbenzene is lowered owing to the consumption of toluene. Therefore,
it was presumed that ZSM-5 type catalyst was not suitable for producing
dibenzylbenzene from toluene and diphenylmethane.
Contrary to the presumption, however, the present inventors have found out
that, despite the existence of toluene, the reaction to produce
dibenzylbenzene proceeds substantially without the formation of xylene.
Furthermore, in addition to dibenzylbenzene, other methyl nuclear
substitution compounds such as methyl and dimethyl derivatives are
produced much.
Accordingly, it is a remarkable fact that xylene is not produced and more
dibenzylbenzenes are produced in the method of the present invention,
which fact has been by no means anticipated in view of the description in
the foregoing patent gazette.
One of the starting materials used in the method of the present invention
is benzene or toluene. These can be used in a mixture.
The other starting material is diphenylmethane or its methyl derivative.
The methyl derivative is namely benzyltoluene or ditolylmethane. These
diphenylmethane, benzyltoluene and ditolylmethane can be used in a
mixture.
Included in the dibenzylbenzenes prepared according to the method of the
present invention are dibenzylbenzene as well as its monomethyl nuclear
substitution compounds such as dibenzyltoluene and its dimethyl nuclear
substitution compounds such as dibenzylxylene.
The conditions for the reaction of benzene or toluene with diphenylmethane
in the present invention are as follows:
In the first place, the catalyst is a crystalline synthetic aluminosilicate
zeolite of 20 or higher in molar ratio of SiO.sub.2 /Al.sub.2 O.sub.3 and
the inlets of main pores thereof are composed of ten-membered oxygen
rings. Such a zeolite is exemplified by ZSM-5 type synthetic zeolite
having the inlets of main pores composed of ten-membered oxygen rings as
well as zeolite zeta 1 and zeolite zeta 2. That is, the zeolite used in
the present invention is characterized in that the inlets of main pores
are composed of ten-membered oxygen rings. Conventional synthetic zeolites
such as zeolite A, erionite and offretite have smaller inlets of
eight-membered oxygen rings. Meanwhile, mordenite, zeolite X and zeolite Y
have larger inlets of twelve-membered oxygen rings.
These conventional zeolites having eight-membered oxygen rings or
twelve-membered oxygen rings are not suitable for use in the method of the
present invention because the structure of them are different from that of
the present invention.
Any of crystalline synthetic aluminosilicates as far as they are 20 or
higher in molar ratio of SiO.sub.2 /Al.sub.2 O.sub.3 and the inlets of
main pores thereof are composed of ten-membered oxygen rings, can be used
as the crystalline synthetic zeolite in the present invention. Especially
preferable ones are ZSM-5 type synthetic zeolites known as ZSM-5, ZSM-11,
ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38 and ZSM-48. All of these ZSM-5 type
synthetic zeolites have the structural characteristic that the inlets of
main pores are composed of ten-membered oxygen rings. Furthermore, most
preferable synthetic zeolite is ZSM-5. The compositions and methods for
preparing these ZSM-5 type zeolites are disclosed in the following patent
gazettes.
ZSM-5: U.S. Pat. No. 3,702,886 British Patent No. 1,161,974 and Japanese
Patent Pub. No. 46-10064
ZSM-8: British Patent No. 1,334,243
ZSM-11: U.S. Pat. No. 3,709,979 and Japanese Patent Pub. No. 53-23280
ZSM-21: U.S. Pat. No. 4,001,346
ZSM-35: Japanese Laid-Open Patent Publication No. 53-144500
Zeolite Zeta 1: Japanese Laid-Open Patent Publication No. 51-67299
Zeolite Zeta 3: Japanese Laid-Open Patent Publication No. 51-67298
The synthetic zeolite having the structural characteristic that the inlets
of main pores are composed of ten-membered oxygen rings, has usually a
high molar ratio of SiO.sub.2 /Al.sub.2 O.sub.3 and the value is generally
20 or higher. In some case, the molar ratio of SiO.sub.2 /Al.sub.2 O.sub.3
is very high, for example, the synthetic zeolite having a molar ratio as
high as 1,600 can be effective. Furthermore, in some case, it is possible
to use a zeolite of substantially no aluminum having a value close to
infinity in the molar ratio of SiO.sub.2 /Al.sub.2 O.sub.3. Such a
"high-silica" zeolite is also included in the definition in the present
invention. This molar ratio of SiO.sub.2 /Al.sub.2 O.sub.3 can be
determined by an ordinary analytical method such as atomic absorption
spectrum analysis. This ratio is defined as the value to be close as
possible to the ratio in the hard skeleton of zeolite crystal but the
aluminum in cation form or other forms contained in binder or channels is
excluded.
The structure of ten-membered rings in the inlets of main pores usually
confirmed by X-ray diffractiometry. For example, the ZSM-5 type synthetic
zeolites which are preferably used as catalysts in the present invention
exhibit characteristic X-ray diffraction patterns particular to them (cf:
the foregoing patent gazettes in detail).
It is, however, possible to employ the values of constraint indexes in
place of the X-ray diffractiometry. That is, the ten-membered oxygen ring
referred to in the present invention can also be defined as the synthetic
zeolites having constraint indexes of 1 to 12. By the way, the practical
determination method of the constraint index is described in Japanese
Laid-Open Patent Publication No. 56-133223. This index shows the degree to
which the pore structure of zeolite crystal restrains the access of
molecules having a cross sectional area larger than that of n-paraffin. In
the determination, as disclosed in the same reference, n-hexane and
3-methylpentane are adsorbed by zeolite under a certain condition and the
index is calculated from adsorbed quantities. Typical values of the
constraint indexes are as follows:
______________________________________
Constraint Index
______________________________________
ZSM-5 8.3
ZSM-11 8.7
ZSM-35 4.5
Amorphous Silica-Alumina
0.6
______________________________________
The method for preparing the zeolite used in the present invention will be
described with reference to the synthesis of ZSM-5.
In the first place, a starting mixture containing tetrapropylammonium
hydroxide, sodium oxide, aluminum oxide, silicon oxide and water, is
prepared. The composition may be made within the range as described in the
foregoing reference. The reaction mixture is then subjected to
hydrothermal synthesis by heating. After the synthesis, the obtained
crystal is baked in the air to obtain ZSM-5 zeolite catalyst.
Tetrapropylammonium hydroxide can be synthesized in situ from
n-propylamine and n-propyl bromide. Aluminum oxide is used herein,
however, it is also proposed to synthesize ZSM-5 containing substantially
no aluminum atom. In the above method, tetrapropylammonium hydroxide is
used, however, it is also proposed as the method for synthesizing ZSM-5 to
use several other organic cations or organic compounds as their precursors
in place of them. Such compounds are exemplified by ammonia,
trialkylmethylammonium cation, triethyl-n-propylammonium cation, C.sub.2
to C.sub.9 primary monoalkylamines, neopentylamine, di- and
trialkylamines, alkanolamines, C.sub.5 to C.sub.6 alkyldiamines, C.sub.3
to C.sub.12 alkylenediamines, ethylenediamine, hexamethylenediamine,
C.sub.3 to C.sub.6 diols, ethylene or propylene glycol, pentaerythritol,
dipentaerythritol, tripentaerythritol, 1,4-dimethoxycyclohexane,
hydroquinone, ethylene oxide and ammonia, n-dodecylbenzene sulfonate,
cyclopentadienyl phthalocyanine complex, 2-aminopyridine, ethylene glycol
dimethyl ether, dioxane, dioxolan, tetrahydrofuran, and carboxylic acids
such as tartaric acid. Furthermore, it is also proposed that, without
adding organic cations or organic compounds as precursors thereof as
described above, ZSM-5 is added as seeds in crystallization.
The zeolite used for the reaction contains metallic ions such as sodium
ions which come from the reaction materials in synthesis. Besides the
sodium as an alkali metal, it is possible to use the one which is ion
exchanged by other alkaline earth metals such as calcium and magnesium and
other trivalent metallic ions. Furthermore, crystalline synthetic
aluminosilicate zeolite such as ZSM-5 type zeolite which is modified with
boron, potassium, phosphorus or their compounds, can also be used. The
methods for these ion exchange and modification can be carried out by a
conventional method.
As described above, the crystalline synthetic zeolite of the present
invention can contain various kinds of metals, however, the synthetic
zeolite which is desirable for the method of the present invention is the
so-called hydrogen-type zeolite in which the metallic ions are substituted
with hydrogen ion. Typical hydrogen-type zeolite is prepared by a process
such that the catalyst containing the organic cations used in the catalyst
preparation is heated for instance at 400.degree. to 700.degree. C. for 1
hour in inert atmosphere and it is then subjected to ion exchange with an
ammonium salt or a mineral acid such as hydrochloric acid, and it is
further calcined, for example, at 300.degree. to 600.degree. C. to be
activated, thereby obtaining the catalyst what is called hydrogen-type
zeolite.
The reaction temperature in the present invention is 170.degree. to
400.degree. C., preferably 200.degree. to 350.degree. C.
When the reaction temperature is lower than the above range, the rate of
conversion of starting material is low. On the contrary, the temperature
above this range is not desirable because a side reaction such as the
formation of xylene is caused to occur.
Even though the reaction can be carried out in vapor phase, however, the
liquid phase is desirable in order to maintain the life of catalyst long.
Furthermore, the vapor phase reaction must be done naturally at higher
temperatures and when the reaction temperature is high, the side reaction
such as the formation of xylene is liable to occur as described above.
Accordingly, the reaction is carried out in liquid phase.
In order to carry out the reaction in liquid phase, it is desirable that
the reaction pressure must be set at a suitable value in which the
reaction system is maintained in liquid phase. This pressure is generally
selected from the range of normal pressure to 50 kg/cm.sup.2.
The type of reaction in the method of the present invention may be either
of continuous flow mode or batchwise mode. In batchwise reaction, the
reaction time is selected from the range of 0.5 to 50 hours, which varies
according to reaction temperature and other reaction conditions. If the
reaction time is shorter than this range, the rate of conversion is low.
On the other hand, when the reaction time is made unnecessarily long, it
is not desirable because the yield of dibenzylbenzene cannot be raised any
more and it rather causes the side reactions.
When the type of reaction is continuous flow mode, the value of LHSV is 0.2
to 20, preferably 0.5 to 10. When the LHSV is smaller than this range, it
is undesirable because side reactions increase and the yield per unit time
length is lowered. Meanwhile, if the LHSV value is too large, it is not
desirable because unreacted reactants are discharged intact from the
reaction system.
In the batchwise reaction, the catalyst is generally used as much as 0.1 to
10% by weight, preferably 0.5 to 5% by weight relative to the mixture of
reactants. If the concentration of catalyst is lower than the above range,
the reaction does not proceed. On the other hand, when the concentration
of catalyst is higher than the above range, the yield of aimed product
cannot always be raised but the excess quantity of catalyst results only
in waste.
The quantity of the monocyclic compound such as toluene to be fed in the
reaction system is 0.2 to 20, preferably 0.5 to 10, in molar ratio
relative to the bicyclic compound of diphenylmethane. When the molar ratio
is smaller than the above range, i.e., when the quantity of monocyclic
compound relative to the dicyclic compound is smaller, the conversion rate
of the raw material is low, which is not desirable. On the other hand,
when an excess quantity of monocyclic compound more than the above molar
ratio is used, it is not desirable either because the quantity per pass of
produced dibenzylbenzene is small.
After the reaction, unreacted monocyclic compounds and unreacted dicyclic
compounds are separated by an ordinary method to obtain the
dibenzylbenzene of the present invention.
The electrical insulating oil of the present invention can be used for
impregnating oil-filled electrical appliances. Exemplified as such
appliances are oil-filled capacitors and oil-filled cables in which at
least a part of their insulating materials or dielectrics are made of
plastics.
The oil-filled capacitor is made by winding a metal foil such as aluminum
foil as an electrode and a plastic film together to obtain a capacitor
element and by impregnating it with an electrical insulating oil through a
conventional method. The conventional paper can be used together with the
plastics film. As the materials for the plastics film, there are
polyolefins such as polyethylene, polypropylene and polymethylpentene, and
polyvinylidene fluoride and polyesters. Among them, the polyolefins are
especially preferable. The electrode may be formed by vacuum-deposited
metal layer and such a capacitor is called as an MF capacitor. The
electrical insulating oil of the present invention is especially suitable
for this MF capacitor.
Furthermore, the oil-filled cable is made by winding a plastics film on a
metallic conductor such as copper or aluminum and it is impregnated with
an insulating oil by a conventional method. As the materials for the
plastics, there are polyolefins such as polyethylene, polypropylene and
polymethylpentene, and polyvinylidene fluoride and polyesters. Among them,
the polyolefins are preferably used, in which insulating paper is
generally used together, or a composite film made of insulating paper and
polyolefin film fused or stuck to the paper or mixed fiber paper of pulp
and polyolefin fiber, is used.
The insulating oil obtained in accordance with the method of the present
invention has a high boiling point, however, the viscosity and pour point
are relatively low. Accordingly, it can be suitably used as an electrical
insulating oil. In addition, the insulating oil of the present invention
can be used together with a conventionally known insulating oil or the
mixture of two kinds or more in an arbitrary ratio of refined mineral
oils; polyolefins such as polybutene; alkylbenzenes such as
dodecylbenzene; diarylalkanes such as diphenylmethane, phenyltolylethane,
phenyl-xylylethane and phenyl-isopropylphenylethane; saturated trimer of
styrene; triaryldialkanes or triarylalkenes such as distyrenated xylene
and dibenzyltoluene; alkylbiphenyls such as isopropylbiphenyl;
alkylnaphthalenes such as diisopropylnaphthalen; and phthalic esters such
as DOP.
The present invention will be described in more detail in the following.
BEST MODE FOR CARRYING OUT THE INVENTION
Example of Preparation of Catalyst
Aluminum sulfate, sulfuric acid, n-propylamine and n-propyl bromide were
dissolved in water and water glass was slowly added to this solution with
stirring to prepare a uniform gel-like slurry. This was fed into an
autoclave and crystallized with stirring at 160.degree. C. for 72 hours.
After the crystallization, the crystals were filtered off and washing with
water and filtration were repeated until the filtrate became neutral to
obtain zeolite ZSM-5 having a molar ratio of SiO.sub.2 /Al.sub.2 O.sub.3
of 70. The obtained zeolite was baked in the air to prepare a catalyst.
The X-ray diffraction pattern was coincident with the data disclosed in
the foregoing patent gazette (Japanese Patent Publication No. 46-10064).
Furthermore, the above-mentioned constraint index was also identical.
Therefore, it was understood that the obtained catalyst had the
characteristic structure of the inlets of main pores comprising
ten-membered oxygen rings.
EXAMPLE 1
The zeolite ZSM-5 prepared in the foregoing Catalyst Preparation Example
was converted into hydrogen type ZSM-5 (12-14 mesh) by the ion exchange
with hydrochloric acid. 200 ml of this catalyst was packed into a 250 ml
reaction vessel and it was dried for 3 hours at 480.degree. C. with the
supply of dry nitrogen.
A mixture in a ratio of 2 moles of toluene and 1 mole of diphenylmethane
was fed at LHSV=1.0, reaction temperature of 310.degree. C. and pressure
of 20 atm (under nitrogen atmosphere).
The obtained reaction mixture was subjected to gas chromatographic analysis
to determine the compositions after certain hours' feed, the results of
which are shown in the following Table 1.
EXAMPLE 2
To a 2 liter autoclave were fed 3 moles of benzene, 3 moles of
benzyltoluene and 20 g of catalyst of H-ZSM-5 and allowed to react for 4
hours at 280.degree. C. and 25 atm.
After the reaction, dibenzylbenzenes were obtained with the results of
analysis of reaction mixture that the rate of reaction of benzyltoluene
was 58% and the selectivity to dibenzylbenzenes was 45%.
EXAMPLE 3
Reaction was carried out in the like manner as in Example 2 except that 3
moles of benzene and 3 moles of ditolylmethane were used. After the
reaction, dibenzylbenzenes were obtained with the analytical results of
the reaction mixture that the rate of reaction of ditolylmethane was 61%
and the selectivity to dibenzylbenzenes was 43%.
COMPARATIVE EXAMPLE 1
Hydrogen type zeolite Y (200 ml, made by Union Carbide, 12-14 mesh) was
packed into a 250 ml reaction vessel and it was dried for 3 hours at
480.degree. C. with the supply of dry nitrogen. A mixture in a ratio of 2
moles of toluene and 1 mole of diphenylmethane was fed at LHSV=1.0,
reaction temperature of 180.degree. C. and pressure of 20 atm (under
nitrogen atmosphere).
The obtained reaction mixture was analyzed by gas chromatography to
determine the composition after 20 hours, feed, results of which are shown
in the following Table 2.
According to the results on zeolite Y, the selectivity to dibenzylbenzenes
was low and the lowering of activity was severe. This lowering of activity
could not be recovered by raising the reaction temperature from
180.degree. C. to 260.degree. C.
TABLE 1
______________________________________
(Example 1)
Composition (wt. %)
Time Di-
of Benzene Ben- tolyl-
Tricyclic
Feed Toluene Diphenyl- zyl- meth- Aromatics
(hr) Xylene methane toluene
ane DBB DBT DBX
______________________________________
20 51.1 11.9 12.8 5.1 4.6 9.6 4.9
80 52.9 12.0 12.3 4.7 4.3 9.1 4.7
120 51.5 12.0 13.1 4.8 4.6 9.2 4.8
160 51.5 12.5 12.8 4.9 4.3 9.2 4.8
200 52.3 13.1 10.9 4.8 4.4 9.5 5.0
300 52.6 13.6 10.9 5.0 4.3 9.0 4.6
500 52.3 14.3 10.9 4.8 4.3 8.8 4.6
800 51.6 15.0 10.8 4.9 4.2 8.8 4.7
______________________________________
Note:
DBB: Dibenzylbenzne
DBT: Dibenzyltoluene
DBX: Dibenzylxylene
TABLE 2
______________________________________
(Comparative Example 1)
Time Composition (wt. %)
of Benzene Di- Di-
Feed Toluene phenyl- Benzyl-
tolyl- Dibenzyl
(hr) Xylene methane toluene
methane benzenes
______________________________________
20 52.2 44.9 2.0 0.4 0.5
______________________________________
EXAMPLE 4
(Recovering of Insulating Oil)
The reaction mixture in Example 1 was recovered and benzene, toluene and
xylene were removed by flash evaporation. A fraction of dibenzylbenzenes
having a boiling point of 350.degree. to 420.degree. C. (converted to
normal pressure) was obtained by reduced pressure distillation, wherein
the separated crystals were filtered off.
(Preparation of Capacitor)
A vacuum metallized polypropylene film of 40 mm in width was used. One side
of the film was applied by a conventional method with a vacuum deposited
zinc layer leaving 3 mm margins. Capacitor elements were made by winding
this metallized film and they were impregnated with the above fraction to
obtain capacitors (hereinafter referred to as "Capacitor A") having a
capacity of 5 .mu.F.
For comparison, similar capacitor elements were impregnated with
phenylxylylethane to obtain comparative capacitors (hereinafter referred
to as "Capacitor B").
(Corona Discharge Characteristic)
According to a conventional method, the corona discharge (partial
discharge) characteristics were determined at 25.degree. C. The results
are shown in Table 3. As shown in the same table, both the corona
discharge characteristics of Capacitor A are higher than those of
Capacitor B.
TABLE 3
______________________________________
Corona Starting
Corona Ending
Capacitor Voltage (V) Voltage (V)
______________________________________
Capacitor A 2,500 2,450
Capacitor B 1,020 890
______________________________________
(Electric Load Test)
According to a conventional method, each of Capacitor A and Capacitor B was
applied with voltages of 120 V/.mu. in potential gradient and the change
in capacity with the passage of time was measured.
As a result, the capacity of Capacitor A was hardly changed after 1000
hours. In the Capacitor B, however, the capacity was reduced by about 15%
after 1000 hours.
By the way, a capacitor impregnated with benzyltoluene was also tested, in
which the change in capacitor after 100 hours was similar to that of
Capacitor B impregnated with phenylxylylethane.
Industrial Applicability
As described above, the present invention provides a method of producing a
novel electrical insulating oil. Furthermore, the insulating oil of the
present invention is most suitable for impregnating MF Capacitors.
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